It is common in many areas of engineering for analysis engineers to size the structural components of a structure or apparatus such that during normal operation the components will not permanently deform, but should the structure experience a load higher than those of normal operation (overload) the components permanently yield and undergo permanent deformation. If detectable the permanent deformation provides an indication to operators or maintenance staff that the structure has experienced above normal loads, allowing further safety checks to be carried out as appropriate.
One such area of engineering is in the aerospace industry and in particular concerning aircraft landing gear. Almost without exception every aircraft landing gear includes at least one pin joint pivotally attaching one component to another, with the pin joint being included in at least one load path of the landing gear. If subject to an overload the pin of the pin joint will permanently bend. However, the amount of bending may be relatively small and therefore difficult to determine just from a visual inspection. Consequently, the deformation may remain undetected which in turn may cause unexpected failure of the landing gear.